Signal interconnect incorporating multiple modular units

ABSTRACT

An interconnect element incorporates a plurality of smaller, substantially identical, interconnect modules. Multiple identical elements can in turn be combined to form larger interconnect networks. Signal paths in the elements can be implemented with optical fibers or electrical conductors.

This application is a continuation of application Ser. No. 09/808,331filed Mar. 14, 2001 now U.S. Pat. No. 6,801,680, which claims thebenefit of the filing date of Provisional Application Ser. No.60/222,352 filed Aug. 1, 2000 and entitled “Building Large OpticalInterconnect From Smaller Modular Units”.

FIELD OF THE INVENTION

The invention pertains to optical cross-connect switches. Moreparticularly, the invention pertains to such switches which incorporatemodular interconnect fabrics.

BACKGROUND OF THE INVENTION

Optical switches are known and are useful in implementing opticalcommunications networks using fiberoptic transmission lines. In suchnetworks, it is at times necessary to switch the optical signals betweenoptical transmission paths.

One known type of optical switch is an optical cross-connect switch. Insuch switches, in a general case, any one of N input lines can becoupled to any one of N output lines.

One known type of cross-connect switch 10 is implementable using theSpanke architecture illustrated in FIG. 1. In a Spanke architecture withN inputs and N outputs, N 1×N switches 12 a, b, c, . . . n are connectedby an interconnect fabric 16 to N 1×N output switches 18 a, b . . . n.

The interconnect fabric 16 has N² total static connections. Oneconnection is between each input-output pair of switches. Therefore, anN×N fabric has a total of N² fibers with N² inputs and N² outputs.

Insertion loss is a major concern in optical cross-connect switches.Although a single stage Spanke design can achieve small insertion loss,this solution creates yet another problem: namely, the difficulty ofcreating the large interconnecting fabric because the fabric contains N²connections.

Methods are known to implement small interconnect fabrics. For example,pre-routed fibers can be sandwiched between flexible plastic sheetssometimes called optical flypapers. They are however very difficult tocreate for N>32. Alternately, the interconnections can be made from N²individual fibers. However, this solution is time consuming to build anddifficult to maintain.

There thus continues to be a need to be able to cost effectively designand implement larger cross connect switches of various sizes. It wouldbe especially advantageous if it would not be necessary to custom createa different interconnect networks for each switch. Preferably, a knowninterconnect design can be reliably and cost effectively manufacturedand could be used to implement a variety of switches.

SUMMARY OF THE INVENTION

A recursive process for creating large signal interconnects from aplurality of smaller, standardized, interconnect modules, which couldincorporate individual optical fibers or electrical conductors, producesinterconnect systems for specific applications using only standardmodular building blocks. In accordance with the method, a first modularK×K interconnect network having K² signal carriers is defined andimplemented. For L inputs,

$\frac{L}{K}$input groups are formed. For M outputs,

$\frac{M}{K}$output groups are defined.

A plurality of

$\left( {\frac{L}{K} \times \frac{M}{K}} \right)$of the first modular interconnects can be used to form an L×M passiveinterconnect network having L×M signal carriers.

A plurality of the L×M, modular interconnects, all of which aresubstantially identical, and all of which are based upon multiples ofthe basic K×K modular interconnect can be combined to form a larger N×Ninterconnect. For example, where L=M, and where N is an integer multipleof M,

$\frac{N}{M}$input groups and

$\frac{N}{M}$output groups result in

$\left( \frac{N}{M} \right)^{2}$M×M modules being needed to implement the N×N connectivity. This type ofnetwork is especially desirable in that economies of scale inmanufacturing, reliability and inventory can be achieved since N×Nnetworks for various values of N can be implemented using multiple,identical K×K basic building blocks which in turn form the larger M×Massemblies which are combined to make the N×N networks.

In one embodiment, an N×N cross-connect switch incorporates a pluralityof substantially identical interconnect modules. A plurality of inputswitches is coupled to N² inputs to the modules. A plurality of outputswitches is coupled to N² output sides of the modules.

In one aspect, the switches can be divided into groups with one set ofgroups associated with the input sides of some of the modules andanother set of groups associated with the output sides.

In another aspect, a switch requiring N inputs and N outputs can beimplemented with multiple identical modules that have K² inputs and K²outputs. The number of required modules is (N/K)². In suchconfigurations, the connectivity between the interconnect, a pluralityof 1×N input switches and a plurality of N×1 output switches can beimplemented using optical ribbon cables. The pluralities of switcheseach contain N switches.

Interconnect modules can be implemented with optical transmittingfibers. Alternately, they could be implemented with electricalconductors.

A method of implementing an N×N cross-connect switch includesestablishing a K×K modular interconnect where K<N. Providing

$\left( \frac{N}{K} \right)^{2}$interconnect modules. Coupling N² inputs to and receiving N² outputsfrom the modules.

In yet another aspect, interconnects implemented from pluralities ofsmaller interconnect modules can in turn become modular building blocksfor even larger interconnect fabrics. In accordance herewith M×M fabricscan be implemented with smaller N×N building blocks. In one embodiment,M is an integer multiple of N.

Non-symmetrical switches with N1 inputs and N2 outputs can beimplemented using K×K interconnect modules where K<N1 and K<N2. With

$\frac{N1}{K}$input groups and

$\frac{N2}{K}$output groups,

$\left( {\frac{N1}{K} \times \frac{N2}{K}} \right)$interconnect modules will be required.

Numerous other advantages and features of the present invention willbecome readily apparent from the following detailed description of theinvention and the embodiments thereof, from the claims and from theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematic of a known cross-connect switch;

FIG. 2 is a block diagram schematic of a modular cross-connect switch inaccordance with the present invention;

FIG. 2A is a schematic diagram of a modular K×K interconnect moduleusable in the switch of FIG. 2;

FIG. 3 is a more detailed schematic diagram of a portion of the switchof FIG. 2 illustrating, in part, connectivity therein in more detail;and

FIG. 4 is a block diagram schematic of a larger interconnect networkincorporating two levels of interconnect modules in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

While this invention is susceptible of embodiment in many differentforms, there are shown in the drawing and will be described herein indetail specific embodiments thereof with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention and is not intended to limit the inventionto the specific embodiments illustrated.

FIG. 2 illustrates a 12×12 cross-connect switch 30 in accordance withthe present invention. It will be understood that while switch 30 hasbeen illustrated for exemplary purposes as a 12×12 cross-connect switch,the number of inputs and the number of outputs is not limited to 12 andcould be N>12. It will be also understood that the inputs to and outputsfrom the switch 30 could be light beams or could be electrical signalswithout departing from the spirit and scope of the present invention.

Switch 30 includes N input switches 32 a . . . 32 n. In the illustratedembodiment, N=12, there would be 12 input switches each of which wouldbe a 1×N type of switch, such as a 1×12 switch. The switch 30 alsoincludes N, N×1 output switches 34 a . . . 34 n. In the illustratedexample in FIG. 2, there would be 12 such output switches which wouldhave 12 inputs and one output at each switch.

The input switches and the output switches are coupled together by aplurality 30′ of substantially identical, static, modular K×Kinterconnect elements 36 a . . . 36 l, K<N. The number of elements is,

$\left( \frac{N}{K} \right)^{2}.$Where N=12 and K=4, then nine 4×4 interconnect elements are required.

Each modular K×K, interconnect element has K² inputs and K² outputs. Arepresentative 4×4 modular interconnect element, such as element 36 i,having 16 inputs that are coupled to 16 outputs is illustrated in FIG.2A. Such modules include a plurality of pre-routed signal carriers 36i-1 optical fibers or electrical conductors. Sixteen signal carriers,for the illustrated 4×4 module, are sandwiched between a pair of plasticsheets, or attached to a single sheet, 36 i-2.

A first plurality of four, 4-way connectors 36 i-3 and a secondplurality of four, 4-way connectors 36 i-4 complete the module theconnectors can be individual or multi-path connectors.

The switch 30, as noted previously has,

$\left( \frac{N}{K} \right)^{2}$interconnect elements, for example, nine 4×4 elements 36 a, b . . . 36l. The input switches are organized into

$\left( \frac{N}{K} \right)$groups, namely 3 groups. With

$\left( \frac{N}{K} \right)$groups, each K×K interconnect module connects a single input group to asingle output group with

$\left( \frac{N}{K} \right)^{2}$group pairs, the number of K×K interconnect modules.

Each group of K fibers such as 40 a, 42 a can be formed of individualfibers, or, of K-wide fiber ribbon cables having K-wide multi-fiberoptical connectors.

Each group includes, for K=4, four 1×12 input switches such as 32 a, 32b, 32 c, 32 d. Groups of K fibers, such as fiber groups 40 a, 40 b, 40 care coupled to K respective inputs each of interconnect elements 36 a,36 b and 36 c. With respect to input switch 32 n, 3 groups of K fibers,40 l, 40 m, 40 n, where K=4, are coupled to respective inputs of K×Kfabric interconnect modules 36 j, 36 k, 36 l. FIG. 3 illustrates in moredetail connections for a portion of the exemplary switch 30.

Output switches 34 a, 34 b, 34 c, 34 d receive groups of fibers, 42 a,42 b, 42 c, and 42 d, where K=4, from K×K interconnect module 36 a. Inthe same way, K×K interconnect module 36 l is coupled via groups of Kfibers, such as 42 k, 42 l, 42 m and 42 n to 1×N, illustrated as 1×12,output switches 34 k, 34 l, 34 m, 34 n.

The architecture of switches such as switch 30 in FIG. 2 is expandableand variable depending on the value of N and the value of K. As analternate, if N=128 and K=32, the number of interconnect modules

$\left( \frac{N}{K} \right)^{2}$is 16. In this instance, each interconnect module would have K² or 32²inputs and the same number of outputs.

The use of multiple, smaller, modular interconnect elements, asillustrated in FIG. 2, makes it possible to build interconnects where Nis a large number, such as for example 128 or larger, using only aplurality of K×K modular interconnect units to form an interconnectingsheet. All of the units can be manufactured so as to be substantiallyidentical.

While the K×K modules 36 a . . . 36 l as disclosed in FIG. 2 canincorporate a plurality of optical fiber lines, similar interconnectscould be implemented using, modular electrical conductors. The abovedescribed signal carrier management process produces interconnects quiteunlike the prior art of either a single pre-routed fabric of N² fibersor N² individual fibers.

The ability to implement increasingly larger switches using pluralitiesof a common interconnect module, to form interconnecting sheets, hasimportant manufacturing, inventory control and quality controlconsequences. Only one, or at most a few, standard fiber or wireinterconnect modules need be manufactured. Hence, the manufacturingprocess can be optimized to produce a few different types of modules.Since manufacturing turn around time can be minimized, less inventoryneeds to be maintained. Finally, quality control can be improved, andenhanced since fewer configurations are being created.

Common interconnect modules are also advantageous from a maintenancepoint of view. In case of a cut or failed fiber or wire only thatrespective modular interconnect element need be replaced.

The K×K interconnect modules of FIG. 2 can be used to implementnon-symmetrical switches. For example, with N1 inputs and N2 outputs,

$\frac{N1}{K}$input groups and

$\frac{N2}{K}$output groups can be defined. These result in

$\left( {\frac{N1}{K} \times \frac{N2}{K}} \right)$input/output group pairs and interconnect modules to implement therequired network. Input switches and output switches can be coupled tothe network.

FIG. 4 illustrates an even larger M×M interconnect 50. Where M is aninteger multiple of N, the interconnect 50 can be implemented using aplurality of N×N interconnect modules, such as the module 30′-i whichcorresponds to interconnect 30′ of FIG. 2. The recursive application ofthe modules 30′, which in turn are based upon the smaller K×K submodulesof FIG. 2, makes the construction of even larger interconnects practicalas they are all ultimately based on two modular interconnect elements

One modular building block is the basic k×k modular fabric element, suchas the element 36 a or 361 illustrated in FIGS. 2 and 3. A secondmodular building block is the N×N composite fabric element 30′ providedthat M is an integer multiple of N. If desired, multiple modular M×Minterconnects an be combined into yet a larger network.

As illustrated in FIG. 4, in the network 50, groups of N signalcarriers, such as the groups 52 a, 52 b . . . 52 n coupled tointerconnect module 30′-1 are combined with groups of N carriers coupledto other modules such as 30′-2 . . . 30′k to form the composite M×Minterconnecting sheet 50. With N carriers in a group, there will be

$\frac{M}{N}$groups resulting in

$\left( \frac{M}{N} \right)^{2}$interconnect modules, such as the module 30′-1 being required. Each N×Ninterconnect module connects a single input group of N to a singleoutput group with

$\left( \frac{M}{N} \right)^{2}$group pairs. Those of skill will understand that the interconnect 50could be combined with appropriate types of input/output switches asdiscussed previously with respect to FIG. 2.

It will also be understood that the M×M interconnect modules 50 can besimilarly combined, as discussed above to create larger interconnectnetworks, again from a plurality of substantially identical M×M modules.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific apparatus illustrated herein is intended orshould be inferred. It is, of course, intended to cover by the appendedclaims all such modifications as fall within the scope of the claims.

1. A signal coupling network comprising: a plurality of substantiallyidentical, static signal interconnect modules, coupling to N inputs to Noutputs, each module having a selected number of K squared module inputsand the same number of module outputs, each of the inputs is coupled toonly one of the outputs by a respective signal carrying conduit witheach output substantially identical to a respective input by a total ofN squared divided by K squared modules.
 2. A network as in claim 1 whichincludes a plurality of input switches, the plurality including apredetermined number of members, each input switch has one signal inputand a plurality of identical signal outputs, the identical signaloutputs are each coupled to a respective one of the inputs.
 3. A networkas in claim 1 which includes a plurality of output switches, each outputswitch has a plurality of signal inputs and one signal output, themembers of the pluralities of signal inputs are each coupled to arespective one of the module inputs.
 4. A network as in claim 2 wherethe plurality of input switches contain as many members as each switchhas outputs.
 5. A network as in claim 1 where each of the members of theplurality of modules is in turn formed of a second plurality of smallerstatic signal interconnect modules, the members of the second pluralityare substantially identical and each contains a second selected numberof inputs and outputs, the second selected number is less than theselected number, each output of the second plurality is substantiallyidentical to a respective input.
 6. A network as in claim 5 where thesecond plurality includes a number of modules corresponding to a ratioof the selected number to the second selected number.
 7. A network as inclaim 1 where the conduits comprise one of, static optical signal paths,or, static electrical signal paths.
 8. A network as in claim 7 whichincludes a plurality of optical switches coupled to inputs of themodules.
 9. A network as in claim 7 which includes a plurality ofoptical switches coupled to outputs of the modules.
 10. A network as inclaim 1 where each module includes a plurality of L×L submodules where Lis less than K and where each submodule includes L squared separate,passive signal carriers which couple each of L squared inputs to adifferent one of L squared outputs with each output substantiallyidentical to a respective input.
 11. A network as in claim 10 where theplurality of L×L modules corresponds in number to K squared divided by Lsquared modules.
 12. A signal coupling network comprising: a pluralityof substantially identical, static signal interconnect modules, eachmodule having a selected number of inputs and a selected number ofmodule outputs, each of the inputs is coupled to only one of the outputsby a respective signal carrying conduit with each output substantiallyidentical to a respective input where the signal conduits are eachbi-directional.
 13. A network as in claim 12 where a number of signalpaths of the module corresponds to the number of inputs.
 14. A networkas in claim 13 which includes a plurality of input switches coupled tothe inputs of the interconnect modules, that plurality has apredetermined number of switches.
 15. A network as in claim 14 where theinput switches each include a single switch input and a number ofoutputs that correspond to the number of switches in the plurality ofinput switches.
 16. A network as in claim 15 where each input switchforms a number of groups of outputs, each group of outputs is coupled toa different module.
 17. A network as in claim 16 where the modules formthe same number of groups as do the input switches.
 18. A network as inclaim 16 where the number of modules corresponds to the number of groupssquared.
 19. A network as in claim 12 where each module comprises asecond selected number of substantially identical static interconnectsub-modules, each sub-module has a third number of inputs and outputs,the third number is less than the second number, each of the thirdnumber of inputs of a selected sub-module is coupled to a respective oneof the third outputs of that sub-module by a separate static signalpath.
 20. A signal coupling network comprising: a plurality ofsubstantially identical, static, signal interconnect modules, eachmodule having a selected number of module inputs and the same number ofmodule outputs, each of the inputs is coupled to only one of the outputsby a respective signal carrying conduit with each output substantiallyidentical to a respective input; and where each of the members of theplurality of modules is in turn formed of a second plurality of smallerstatic signal interconnect modules, the members of the second pluralityare substantially identical and each contains a second selected numberof inputs and outputs, the second selected number is less than theselected number, each output of the second plurality is substantiallyidentical to a respective input.
 21. A signal coupling network as inclaim 20 where the second plurality includes a number of modulescorresponding to a ratio of the selected number to the second selectednumber.